Home efficiency
Condensation, damp and ventilation
Most damp in UK homes is condensation: moisture from cooking, washing and breathing settling on cold surfaces. Good ventilation and steady heating reduce it, but other kinds of damp need repairs.
Updated 2 October 2026 · energy.org.uk editorial team
Signs of damp
- Water on windows and cold walls, especially in the morning
- Black mould, often in corners, behind furniture and around windows
- A musty smell
- Peeling paint or wallpaper, crumbling plaster or damaged skirting
- A tidemark low on a wall, or damp patches that do not dry out
The three main kinds
- Condensation: moist air meeting cold surfaces. It is usually worst in kitchens, bathrooms and bedrooms, and in winter.
- Rising damp: ground water rising through walls, usually up to about a metre, leaving a tidemark.
- Penetrating damp: water getting in through the walls or roof, often from leaking gutters, pipes or damaged brickwork. Patches often grow after rain.
Do
Practical next steps
- Keep trickle vents in windows open.
- Run extractor fans while cooking or showering, and for at least 15 minutes afterwards. Keep lids on pans.
- Dry clothes outside where you can, or in a room with the door closed and a window open or a dehumidifier running.
- Leave a gap between furniture and outside walls.
- Wipe condensation off windows in the morning.
- Keep the home steadily warm rather than letting rooms get very cold.
A dehumidifier helps in a room that stays damp; see what one costs to run in the appliance calculator.
When to get help
If damp patches keep growing, there is a tidemark, or damp follows rain, the cause is probably a leak or a building fault rather than condensation. Have it inspected. Renters should report damp and mould to their landlord in writing.
Take care
Important limitations
- Insulating or draught-proofing a home without keeping enough ventilation can make condensation worse.
- Treating mould on the surface does not fix the cause.
- Persistent mould can harm health, especially for children, older people and anyone with breathing problems.
Related tools and guides
Sources
Official sources checked 2 October 2026.